Marine Jet drives propelling a vessel based on water jet propulsion have long been known and used due to certain advantages over the traditional external ship's propeller. An engine driven impeller, rotating inside an impeller housing pumps water from below the vessel through an intake duct, then pressurizes and expels said water through a diffusor housing and a nozzle horizontally behind the vessel. A typical example of such a conventional marine jet drive is seen in U.S. Pat. No. 3,935,833, which shows a pump, that may be driven vertically or horizontally and is positioned near the bottom and transom of a marine vessel. The conventional jet propulsion systems have certain general advantages that make them especially attractive under circumstances where a conventional ship's propeller would be exposed to damage by contact with underwater objects. A jet drive has the further advantage that it does not produce appendage drag and is safe for swimmers and animals who could be hurt by the rotating blades of an external propeller.
The known jet drives have, however, certain drawbacks compared with the conventional external propeller propulsion system. A major drawback is caused by the large size and weight of the steering and reversing deflectors, used in conventional jet drives, as well as a lack of ability to steer the vessel in case of loss of engine power.
Transom interference with forward water flow during reverse operation hinders the otherwise good reverse and maneuvering capability of a conventional marine jet drive; likewise, trim planes are incompatible in conjunction with conventional jet drive reversing systems because said planes block said forward water flow. Another drawback is the placement of steering and reversing hydraulic control cylinders, hydraulic hoses, position feedback cables, and lubricating hoses outside the vessel, exposed to water and the weather where corrosion and marine growth damage exposed rod ends, hydraulic seals and hoses.
Further, because of the recited deficiencies, conventional jet drives require time consuming disassembly and frequent servicing and repair.
It is accordingly a primary object of the present invention to provide a marine jet drive propulsion system that overcomes the disadvantages of the known jet drives. In particular, the jet drive according to the present invention provides a combined steering and reversing mechanism that is lighter in weight and smaller in dimension and has improved performance. U.S. Pat. No. 4,538,997 displays a reversing means, whereby a single, centrally located reversing scoop moves up from the bottom of a steering tube, deflecting water for reversing down and forward. The present invention uses a single fixed split duct with right and left ports or twin reverse ducts, fastened to left and right steering deflectors, sending water flow forward and angled away from the intake duct during reverse operation and is in concept different from the referenced patent.
A set of steering vanes may be provided, attached to the outer surfaces of the reverse ducts, as they are fastened to the steering/reverse deflectors and move with said deflectors. U.S. Pat. No. 3,982,494 provides for an auxiliary rudder that is actuated by the jet pump pressure and swings out of the way at higher speeds, to reduce drag. The present invention uses the reverse ducts, also a subject of the present invention, to rigidly support the steering vanes.
Also provided is reverse operation eliminating backwash against the transom using a reverse/trim plane in close proximity to the jet drive, that retracts to a position above the reverse ducts during reverse operation forcing all forward water flow underneath the vessel. In forward direction the reverse/trim plane may be adjusted like a trim plane.
The mechanical or hydraulic controls, operating the combined steering/reversing deflectors, the nozzle aperture inserts and reverse/trim plane are placed inside the vessel to avoid marine growth and weather exposure. They are however attached to the impeller housing forward flange. Sliding control rods with water seals at the transom connect said deflectors, aperture inserts and reverse/trim plane to the mechanisms inside. This allows the installation and adjustment of said mechanisms to be done at the factory, without the need of having the intake duct present. Additionally, these control mechanisms have a park position whereby all control rods are pulled into their retracted positions, preventing damage from corrosion and marine growth to the sealing surfaces, while the vessel is idle for extended periods of time. Even in the event of failure of said water seals, only water will leak into the vessel and no oil will leak into the water, avoiding pollution and hydraulic system failure.
Further, construction, operation, weight reduction and maintenance features are part of the invention, as will be described in detail in the following presentation with appended drawings and claims.